The present Invention is directed to a sliding gear drive with a first sliding element in connection with a motor and a second sliding element, engaged by a variable load, and in engagement with the first sliding element by a wedge-shaped transmission connection.
Sliding gear drives are generally used where, for spatial or other functional reasons, a direct and linear force flow deflection is desired. In addition, sliding gear drives offer the capability of a path reduction/power ratio, and in particular the advantage of being able to interrupt the gear connection after a shifting motion and locking of the driven sliding element, for example, in conjunction with a step function, the driving sliding element can be returned to its starting position.
As an example, a data card unit represents a typical application case. In a data card unit, a data card carrier, in a read/write position of the data card, must be shifted against the action of a spring into a removal position when the data card is to be removed. In this position, a locking of the data card carrier takes place. When inserting a data card in such an arrangement, the data card carrier is unlocked and displaced my means of a spring into the read/write position. Accordingly, in the read/write position, it lies against a stop under the action of the spring.
If, for example, the data card unit is used in a commercial vehicle, then it is necessary, to insure exact positioning or contacting of an inserted data card and to exclude the risk of positional changes due to operationally induced vibrations, that the data card carrier must be under a relatively large contacting pressure in the read/write position. As a result, the motor, moving the data carrier by means of the sliding gear drive, is acted upon by a relatively large initial load and by an additional transporting load, which increases with the shifting of the data card carrier. Further, the data card is to be removed in a relatively short time whereby an appropriately powerful motor must be used. The high costs resulting from such an arrangement are not acceptable, especially if it is located in the instrument area of a vehicle. This means that motors, suitable with respect to torque, cannot be used. In addition, as a result of various voltage drops, the full voltage of the vehicle battery is not available and the current consumption is limited for safety reasons as well as legal provisions.
Of course, the torque required by the motor can be reduced owing to the fact that a high transmission reduction is provided between the motor and the driving sliding element and/or that the wedge angle of the sliding gear drive is constructed relatively flat. In each of these cases, the waiting time for removing data cards is unacceptable. Moreover, additional space is required and, due to the transmission expansion, the costs are increased.
Therefore, a primary object of the present invention is to gain a sufficiently short actuation of the driven sliding element in geared connection and formed by a sliding gear drive and acted upon with a variable load even when the driving power is limited and to achieve the object at a cost which can be justified for continuous production.
In accordance with the present invention, a wedge gear connection is provided so that the motor is acted upon by a torque not proportional to the variable load.
In a preferred embodiment of the wedge gear connection, the wedge surfaces of the sliding elements, interacting during transmission, have a curved configuration in the sliding direction.
Further advantageous developments of the invention are evident from the dependent claims.
The advantage afforded by the invention is that a variable wedge angle between the sliding elements is particularly effected in that it can be accomplished without any additional technical effort, that is, without additional components and that only the basic or initial load has to be taken into consideration for the torque required to drive the motor. A suitable curved shape for the interacting wedge surfaces, a torque compensation and optionally, a constant torque requirement for the driving motor can be created even in the case of loads which do not increase linearly. Furthermore, the inventive arrangement can also be used for a case in which a constant load to be moved at different speeds and torque, required by the driving motor, is to be kept essentially constant.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by it use, references should be had to the drawings and description matter in which there are illustrated and described preferred embodiments of the invention.